CVE-2026-89908
HighCVSS 8.8Summary
In the Linux kernel, kvm_arch_prepare_memory_region() in KVM for LoongArch computes arch flags for a memslot only for KVM_MR_CREATE and KVM_MR_MOVE, returning early for KVM_MR_FLAGS_ONLY. Since the generic code allocates a zeroed memslot, after a KVM_MR_FLAGS_ONLY update the arch flags are cleared, potentially causing guest memory to be mapped to wrong host pages. The fix carries arch flags over from the old memslot for KVM_MR_FLAGS_ONLY.
Risk Assessment
This can lead to guest memory being mapped to wrong host pages, causing data corruption or potential information leakage between VMs. It affects KVM on LoongArch environments.
Recommendation
Update the Linux kernel to a version containing the fix. Avoid dynamically changing memslot flags (e.g., KVM_MEM_LOG_DIRTY_PAGES) until patched.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: LoongArch: KVM: Preserve memslot arch flags on KVM_MR_FLAGS_ONLY kvm_arch_prepare_memory_region() computes new->arch.flags, i.e. whether a memslot is KVM_MEM_HUGEPAGE_CAPABLE or KVM_MEM_HUGEPAGE_INCAPABLE, only for KVM_MR_CREATE and KVM_MR_MOVE, and returns early for every other change. But the generic code allocates a zeroed memslot for every change and never copies old->arch, so after a KVM_MR_FLAGS_ONLY update, e.g. toggling KVM_MEM_LOG_DIRTY_PAGES for live migration, the active memslot has arch.flags == 0. With both flags clear, fault_supports_huge_mapping() falls through to the alignment check on the HVA range alone, which no longer verifies that the GPA and HVA have the same offset within a PMD. A memslot that was marked KVM_MEM_HUGEPAGE_INCAPABLE because of a GPA/HVA offset mismatch can then be mapped with PMD entries on read faults, and since kvm_map_page() aligns the gfn and the pfn independently, the guest ends up accessing the wrong host pages, exactly the "d -> f, e -> g" case described in the comment above the check. Carry the arch flags over from the old memslot for KVM_MR_FLAGS_ONLY, as the GPA, HVA and size are guaranteed to be unchanged for that case.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS